The present invention relates to a measuring apparatus and a measuring method for concrete-forming materials which measure water and aggregate whose moisture state is not uniform.
When kneading concrete-forming materials on site, it is necessary to manage appropriately an amount of water since it has a strong influence on strength of concrete and the like. However, a moisture state of the aggregate, which is a concrete-forming material, changes with storage situations, climatic conditions, and the like. Therefore, if aggregate in a wet condition is used, an amount of water in concrete will increase by an amount of surface water of the aggregate. On the other hand, if aggregate in a dry state is used, an amount of water in concrete will decrease by an amount of water absorbed into the aggregate according to an effective absorption of the aggregate.
Therefore, in order to make concrete as a specified mix, it becomes very important in a case of kneading of concrete-forming materials to correct the amount of water according to a dryness-and-moisture grade of aggregate.
Here, aggregate generally stored, especially fine aggregate is wet in many cases. Therefore, it is common to measure a percentage of surface moisture of aggregate beforehand, and to adjust the amount of water based on the percentage of surface moisture measured.
A percentage of surface moisture, which is an index pertaining to dryness and moisture of aggregate, is obtained by dividing a mass of surface water of the aggregate (water adhering to a front face of the aggregate in a wet condition) by mass of the aggregate in a saturated surface-dried condition. Here, the aggregate in the saturated surface-dried condition means aggregate whose front face is dry and whose core is saturated with water.
And conventionally, in measurement of such percentage of surface moisture, a small amount of sample is extracted from a storage container called a stock bin in which aggregate is stored for measuring the mass of the sample and the mass of the sample dried completely. Next, the percentage of surface moisture was computed by using these measured values and a coefficient of water absorption of the aggregate measured beforehand.
However, by such a measuring method, since a percentage of surface moisture of aggregate in the stock bin is guessed from few samples, accuracy is inferior. On the other hand, in order to measure the mass of aggregate dried completely, heating by a burner and the like is needed. Therefore, it is impractical to measure the mass of aggregate dried completely whose amount is near an actually used amount since much time and expense are needed.
In order to avoid such a problem, an operator checks a kneading situation visually or adjusts an amount of water by using an electric-current value of a mixer. However, these methods have low accuracy primarily. Therefore, as a result, in order to secure strength of concrete, it is necessary to expect nearly twenty superfluous factors of safety, and this leads to an uneconomical mix proportion.
Especially in mixing a plurality of aggregates, kinds of which are different in terms of density and grading, for example, the problem mentioned above becomes still more serious.